Skeletal muscle (SKM) microvasculature has been studied extensively with respect to respiratory gas and nutrient exchange, volume distribution, and blood flow control, into and within the organ, in health and disease. This R21 is in response to a PFA requesting development of models for the study of function in males and females. This is terribly important as most studies of SKM have been conducted in males (animals and humans) with the presumption that the data apply equally to both sexes. Evidence from multiple studies accumulated over the last decade is making it clear that this assumption in error. One model used widely for in vivo study is the rodent cremaster, a thin muscle derived from the abdominal wall that raises and lowers the testes. Surprisingly, no microvascular skeletal muscle preparation of equivalent metabolic and fiber type substitutes presently for the cremaster that facilitates study of both males and females. This proposal aims to rectify this lack by validating the abdominal wall skeletal muscle preparation in males and female rodents. The hypothesis is that microvascular skeletal muscle functions do not differ between age-matched males and females of the same species. Accordingly, 3 aims will be carried out in in situ and isolated abdominal muscle microvessels from age- and strain-matched female and male mice: Aim 1 will assess whether sexual dimorphism exists with respect to blood flow regulation from measures from microvascular diameter to selected endothelium-dependent and -independent agents. Given recent data we expect to reject our hypothesis as we anticipate that a) arterioles from males will develop greater basal tone and b) the dose-response relationship for the endothelium-dependent dilation will differ between males and females. Aim 2 will assess whether sexual dimorphism exists with respect to exchange regulation from measures from measures of microvessel solute permeability (Ps). Given our data, we expect to reject our hypothesis as we anticipate that a) venules from males will be leakier than those from females, b) basal arteriole and capillary barrier properties will not differ by sex, and c) the vasoactive agents will produce a variety of exchange responses reflecting differences in sex-specific mechanisms regulating solute distribution between the vascular and tissue compartments of males and females. Aim 3 will compare the sex, age, organ and species matched diameter (Aim 1) and exchange data (Aim 2) from microvessels as they lay in the living tissue and following isolation from the tissue. This is an incredibly opportunity to make these comparisons as not all tissues are amenable to study in situ and it is assumed that the data from the isolated vessels reflect the behavior in the tissue. Data from this project will form the foundation for future genetic, biochemical, and physiologic studies of microvascular function in males and females. It is imperative that we validate a model for study of microvascular function in both sexes to understand intelligently the sex-dependent mechanisms regulating vascular function in health and dysfunction in disease. With the knowledge the foundation, and provide rational means for prevent and treating vascular disease specific to the needs of males and females.) PUBLIC HEALTH RELEVANCE: This project is to develop and validate a skeletal muscle model for the study of the primary functions of the smallest blood vessels in age-matched male and female animals of the same species, the mouse. The 2 primary functions of the microcirculation 1) blood flow to metabolizing tissue, and 2) the movement of nutrients from blood to tissue as well as the removal of wastes from tissue to blood, appear to differ between males and females in health and cardiovascular disease including hypertension and secondary to type 2 diabetes. As materials distribute themselves between blood and tissue, so too will fluids move between compartments;thus if exchange regulation differs between males and females it is likely that volume distribution will also differ. Therefore it is imperative to have access to a model to learn the differences and similarities between the sexes as the data from males, disease incidence and severity and subsequent treatment strategies will not apply equally to females.